The invention relates to a method for feeding thermal energy into an exhaust emission control unit connected in the exhaust gas system of an internal combustion engine, in particular a diesel engine, by heating the exhaust gas flowing to the exhaust emission control unit to a SET temperature. The exhaust gas discharged from the internal combustion engine is heated to the SET temperature by converting hydrocarbons (HC) metered into the exhaust gas flow at two oxidation catalytic converters connected in series—in the direction of the flow of the exhaust gas. The first oxidation catalytic converter in the direction of the flow of the exhaust gas to the internal combustion engine is arranged in a secondary system, and the second oxidation catalytic converter which is downstream of the former converter is arranged in the exhaust gas system after the merging of the main and secondary systems.
Internal combustion engines, today diesel engines in particular, comprise control units that are connected in the exhaust gas system in order to reduce harmful or undesired emissions. Such a control unit can bean oxidation catalytic converter, a particle filter and/or an SCR stage, for example. A particle filter is used to collect soot particles discharged by the internal combustion engine. The soot that is entrained in the exhaust gas accumulates on the upstream side surface of the particle filter. A regeneration process of is triggered when the soot load of the particle filter reaches a sufficient level to prevent an excessive increase in the exhaust gas counter pressure during the course of the successive soot accumulation and/or to prevent the risk of clogging the filter. In this regeneration process, the soot that accumulates on the filter is burnt off (oxidized). The particle filter is regenerated after the completion of such a soot oxidation. Only a noncombustible ash residue remains. For a soot oxidation to occur, the soot must be at a certain temperature. As a rule, this temperature is approximately 600° C. If the oxidation temperature has been reduced by an additive or by providing NO2, the temperature at which such a soot oxidation starts can be lower. If the soot is at a temperature below its oxidation temperature, then thermal energy has to be fed into the system, in order to be able to actively trigger a regeneration. An active regeneration can be started using engine-internal measures, by changing the combustion process so that the exhaust gas is discharged at a higher temperature. However, post-engine measures are, preferable in order to produce an active regeneration in numerous applications, particularly in the non-road field. In many cases, it is not possible in the context of exhaust emission control to have an influence on the engine-based measures.
From DE 20 2009 005 251 U1, an exhaust emission control unit is known, wherein, the exhaust gas system is divided into a main exhaust gas system and a secondary exhaust gas system, for the purpose of actively producing the regeneration of a particle filter. A catalytic burner is connected in the secondary system, by which the partial exhaust gas flow flowing through the secondary system is heated and subsequently merged with the partial exhaust gas flow flowing through the main system. This results in the mixed exhaust gas mass flow being at a clearly higher temperature. The increase in the temperature of the exhaust gas flow is used to heat the soot accumulated on the upstream side of the particle filter to a temperature sufficient to trigger the regeneration process. An oxidation catalytic converter having an upstream hydrocarbon injection, which is arranged in the secondary system, is used as catalytic burner. An exhaust gas flap which can set the cross-sectional area that allows free flow in the main system can be used for controlling the exhaust gas mass flow flowing through the secondary system. An electro-thermal heating element is connected upstream of said converter for heating the oxidation catalytic converter connected in the secondary system to its light-off temperature, namely the temperature at which the desired exothermic HC conversion starts to occur on the catalytic surface. The latter heating element is operated when this oxidation catalytic converter has to be heated to its light-off temperature. This document also describes that the catalytic burner connected in the secondary system can be oversprayed in order to feed hydrocarbons to a second oxidation catalytic converter directly upstream of the particle filter in the flow direction. This allows these hydrocarbons to react with the same exothermic reaction on the catalytic surface of this second oxidation catalytic converter. In this manner, a two-step heating of the exhaust gas can be carried out in this previously known emission control installation. The exhaust gas flowing out of the second oxidation catalytic converter is then at the required temperature in order to heat the soot accumulated on the upstream side of the particle filter sufficiently so that the soot oxidizes.
Similarly, it can be desirable to increase the temperature of other exhaust emission control units, for example, of an oxidation catalytic converter or of an SCR stage, in order to bring the latter more rapidly to their operating temperature.
Based on this discussed prior art, the aim of the invention is to propose a method by means of which, in particular during the dynamic operation of an internal combustion engine, for example,
of a diesel engine in a vehicle, in a short time, and at least largely uninfluenced by changing circumstances in the exhaust gas system, such as, for example, changing exhaust gas mass flows,
a regeneration process can be triggered in a targeted manner in order to regenerate a particle filter.